Evaluation of synthetic and biological HCV reference materials with three commercial HCV quantitative assays. Serial dilutions of the Paul Erlich Institute (PEI) regional HCV standard (80,000 IU/ml), high titer plasma, Armored RNA Quant HCV and synthetic HCV RNA transcript were tested using the RealTime HCV (A), COBAS AmpliPrep/COBAS TaqMan HCV (B), or VERSANT HCV RNA 3.0 assays (C). All test specimens were shipped and stored below −70°C. The HCV Armored RNA was prediluted, shipped, and stored in base human serum. Other specimens were formulated by each laboratory using the same base matrix immediately after thawing of the stock materials. The synthetic HCV RNA transcript was diluted in the presence of lysis reagent to inhibit potential degradation of the RNA by serum nucleases. At least six replicates of each dilution were tested in three independent runs with each assay. The synthetic materials were formulated in copies/ml of base matrix (2.5 × 103, 5 × 103, 1 × 104, 1 × 105, 1 × 106, and 1 × 107 copies/ml) and converted to IU/ml (IU/ml = copies/ml × 5). Ct, threshold cycle; RLU, relative light units.